This is a continuation in part of copending patent application Ser. No. 860,027, filed September 22, 1969.
This invention relates to the production of phenolic compounds, e.g. phenol itself. More particularly it relates to the production of a phenolic compound from a corresponding aromatic aldehyde; that is, it relates to a method for replacing the carbonyl group of an aromatic aldehyde with the phenolic hydroxy group.
In a particularly useful embodiment, the invention relates to a method for producing phenol from benzaldehyde, which in turn is obtained by the vapor phase oxidation of toluene to form either benzaldehyde itself or its equivalent precursor benzyl alcohol. The benzyl alcohol is oxidized to benzaldehyde, which then is oxidized to phenol.
Taking phenol itself as an example of an industrially useful phenolic compound, the presently-available industrial methods for producing it synthetically comprise (a) sulfonation processes, (b) chlorination processes, (c) the alkylation of benzene to cumene followed by conversion to cumene hydroperoxide which is then split to phenol and acetone, and (d) a two-stage liquid-phase oxidation process in which toluene is catalytically oxidized to benzoic acid which then, in a second stage, is further oxidized to phenol. While these processes are all commercially useful, each has some drawback. For example, the sulfonation and chlorination processes, as well as the liquid-phase oxidation process, entail difficulties due to equipment corrosion, while the cumene hydroperoxide process has, among other drawbacks, the limitation that its economics are dependent in large part on profitable disposal of the by-product acetone. The benzoic acid process is also subject to operating difficulties due to formation of tars in the second reaction step.
Other than the above-identified two-stage oxidation process, processes for producing a phenol by oxidatively converting an alkyl substituent in an aromatic compound are not known.
The art also contains no clear teaching that an aromatic aldehyde, such as benzaldehyde, can be oxidized to form the corresponding phenol in appreciable yield. Barnard and Ibberson, in a paper published in "Combustion and Flame", Vol. 9, pages 149-157 (June, 1965), discuss the gaseous oxidation of toluene and report the presence of trace quantities of phenol in the oxidation products. Yields of phenol were very small, however, and methods for obtaining significant yields of phenol from benzaldehyde are not set forth. These workers also report the formation of tarry deposits in the reaction system.
It is an object of the present invention to provide a method for converting an aromatic aldehyde to the corresponding phenolic compound. It is another object to provide a method for accomplishing said conversion by straightforward oxidation methods which do not require the use of any catalyst. It is another object to provide a method whereby said oxidation can be accomplished with minimum product loss due to tar formation. It is yet another object to provide a method for converting an alkyl benzene to the corresponding phenolic compound by way of an aromatic aldehyde derived from the alkybenzene.
It is particular object to provide an improved process for converting toluene to phenol, in which process the toluene is converted to benzaldehyde which is then further converted to phenol.
Other objects of the invention will be apparent from the following detailed description and examples.